Electrophotographic apparatus employing atmospheric pressure to hold the film in contact with the photoconductor



. LBRODIE 3, ELECTROPHOTOGRAPHIC APPARATUS EMPLOYING ATMOSPHERIC INCONTACT WITH PRESSURE TO HOLD THE FILM THE PHOTOC UC Filed Feb. 1

FIG. I

|4- -5oov HI] Q u an Q, 1" I W l hm. pl H1 "III" 1/ IIV .WORQBRODIE vATTORNEY United States Patent O 3,506,348 ELECTROPHOTOGRAPHIC APPARATUSEM- PLOYING ATMOSPHERIC PRESSURE TO HOLD THE FILM IN CONTACT WITH THEPHOTOCONDUCTOR Ivor Brodie, Palo Alto, Calif., assignor to VarianAssociates, Palo Alto, Calif., a corporation of California Filed Feb.10, 1967, Ser. No. 615,134 Int. Cl. G03b 27/20, 29/00; G03g 15/00 US.Cl. 355-16 2 Claims ABSTRACT OF THE DISCLOSURE In electrophotographicapparatuses, with a photoconductive plate illuminated by a photon image,a vacuum member is positioned to hold the recording medium against theplate. T he. electrographic recording paper having a charge retentivesurface and a conductive backing is placed against the photoconductiveplate with the charge retentive surface adjacent the photoconductor. Apotential as of 500 v. is applied across the. photoconductor and theelectrographic paper for a short time during which the photoconductor isilluminated by the photon image to be reproduced. The photoconductorbecomes conductive in the regions which are illuminated, thereby causingan electric charge image, corresponding to the image being reproduced orphotographed, to be deposited upon the. charge retentive surface of theelectrographic paper. The charge image is subsequently developed byconventional electrographic toner development methods. During the timethe charge image is being deposited on the electrographic paper, thepaper is held in nominal contact with the photoconductive plate bydrawing a partial vacuum between the photoconductive plate and theelectrographic paper such that atmospheric pressure holds the paperagainst the photoconductor. A groove around the marginal edge of thephotoconductive plate is connected to the suction side of an air pumpfor drawing the partial vacuum between the photoconductive plate and theelectrographic paper. A rubber O-ring encircles the groove and aperforated pressure plate clamps the paper against the O-ring to sealthe outside marginal edges of the groove to the paper.

DESCRIPTION OF THE PRIOR ART Heretofore, electrophotographic cameras,and printers have been proposed wherein a photoconductor serves totransform a photo image to be reproduced into a charge image pattern ona charge retentive surface of a sheet or strip of electrographicrecording material. An example of such apparatus is described in US.Patent 2,825,814 issued Mar. 4, 1958. In this prior art, it is describedthat the charge retentive surface should preferably be spaced by 1 tomicrons from the surface of the photoconductor and it was proposed thata finepowder, dusted over the surface of the photoconductor, could helpprovide the proper spacing.

It has been discovered that the surface roughness of of thephotoconductor and electrographic paper is suflicient, taken alone, toprovide the minute air gap between th photoconductor surface and thecharge retentive surface of the recording web when the two are innominal contact. It has also been discovered that the two surfaces arepreferably pressed together into nominal contact over essentially theirentire mutually opposed areas in order to assure uniformity in theresultant transfer of charge images to the recording web.

SUMMARY OF THE PRESENT INVENTION The principal object of the presentinvention is the pl'OVlSlOll of an improved electrophotographicapparatus.

One feature of the present invention is the provision, in

an electrophotographic device, of means disposed at the. marginal edgesof the photoconductive imaging plate for drawing a partial vacuumbetween the plate and the charge retentive surface of a recording weboverlaying the plate, whereby atmospheric pressure exerted on the backside of the recording we'b presses the web into nominal contact with thephotoconductive plate to assurev unifom charge transfer to the web.

Another feature of the present invention is the same as the precedingfeature wherein the means at the marginal edge of the photoconductiveplate for drawing the partial vacuum includes a groove encircling thephotoconductive plate, such groove being in gas communication with thesuction side of an air pump.

Another feature of the present invention is the same as any one or moreof the preceding features including the provision of an elastic gasketencircling the marginal edges of the photoconductive plate incooperative relation with a pressure plate at the backside of therecording web such that when the pressure plate is forced toward thephotoconductive plate it serves to make a gas tight seal between thegasket and the web at the marginal edge of the photoconductive plate topermit a partial vacuum to be drawn between the web and thephotoconductor.

Other features and advantages of the present invention will becomeapparent upon a perusal of the. following specification taken inconnection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional viewof an electrophotographic camera employing features of the presentinvention, and

FIG. 2 is a sectional view of a portion of the structure of FIG. 1 takenalong line 22 in the direction of the arrows rotated clockwise with theback of the camera including the paper transport apparatus removed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2,there is shown an electrophotographic camera 1 employing features of thepresent invention. The camera 1 includes a dark box 2 having a lens 3and shutter 4 at one end and a photoconductive plate 5 disposed in thefocal plane at the other end of the box 2.

The photoconductive plate 5 is supported from a glass plate 6 via theintermediary of an optically transparent conductive electrode 7sandwiched therebetween. The glass plate 6 is cemented at its marginaledges to a lip portion 8 of a relatively thick annular metallic flangemember 9.

A groove 11 encircles the margin edges of the photoconductive plate 5and is defined by a space between the surrounding flange 9 and themarginal edges of the sandwiched plate assembly 5 including glass plate6, electrode 7 and photoconductive plate 5. An air pump 12 has itssuction side connected into the groove 11 by means of a gas passageway13 for drawing a partial vacuum, as of 20 inches of Water, on the groove11. An elastic O-ring 14, as of rubber, encircles the groove 11 and isretained, as by cement, within a shallow groove in the flange 9.

A housing member 15 is hinged to the flange 9 at 16. A perforatedconductive pressure plate 17 is carried from the housing 15 via springs18. A cam 19 is eccentrically pivoted about shaft 21. The shaft iscarried at its ends from the housing 15. The cam 19 includes a lever arm22 which extends out of the housing 15 through a slot 23 therein.

A roll of electrographic recording paper 24 supplies a strip ofrecording paper which is threaded between the pressure plate 17 and thephotoconductive plate 5. The roll of paper 24 is supported on a shaft25. The shaft 25 is supported at its ends by the housing 15. Theelectrographic paper comprises an electrically conductive paper backingwhich supports a thin dielectric film. In a typical example the film isonly 4 microns thick. The dielectric film forms the charge retentivesurface of the paper 24. The charge retentive film is disposed facingthe photoconductive plate 5.

A voltage source 26, as of -500 v., is connected across thephotoconductive plate and electrographic paper 24 by having the negativeterminal of the supply 26 connected to the conductive electrode 7 andits positive terminal grounded. The pressure plate 17 is also grounded.A timer switch 27 is connected between the negative terminal of thesupply 26 and the conductive electrode 7.

In operation, the shutter 4 is closed and a length of paper 24 is pulledfrom the roll 24 through the housing until an unexposed length of paper24 overlays the back of the photoconductive plate 5. The air pump 12 isstarted and the pressure plate lever 22 is moved to the upper position,indicated by phantom lines, to cause the marginal edges of the pressureplate 17 to push the paper 24 against the rubber O-ring 14. Thisproduces a gas tight seal between the paper 24 and the flange 9. Theseal encircles the outer marginal edge of the groove 11.

With the seal completed, the air pump 12 draws a partial vacuum, as ofinches of water, on the space between the paper 24 and thephotoconductive plate 5. The reduced pressure on the photoconductor sideof the paper 24 causes atmospheric pressure on the other side of thepaper 24 to press the paper flat against the photoconductive plate 5, asindicated by dotted line 31. This pressure produced nominal contactbetween the charge retentive surface of the paper 24 and thephotoconductive plate 5 over essentially the entire area of the plate 5.The presently accepted theory of operation requires a minute air gap, onthe order of 10 microns, between the charge retentive surface and thephotoconductive surfaces. It is believed that the surface irregularitiesof the photoconductor 5 and of the dielectric film surface of the paper24 are of a magnitude on the order of a few microns. Thus, it isbelieved that these minute surface irregularities prevent the twosurfaces from actually coming into complete physical contact and therebyprovide the minute air gap. Thus, the term nominal contac has beenemployed to described the contact between these two surfaces and suchterm is defined to mean that the abutting surfaces have a minute air gaptherebetween of on the order of 10 microns.

The partial vacuum drawn on the paper 24 from the edges of the plate 5assures that no air pockets develop which would otherwise preventuniform large area nominal contact between the paper 24 and the plate 5.The pressure plate 17 is in electrical contact with the conductive paperbacking of the paper 24. The pressure plate 17 may be relativelyflexible and a leaf spring, not shown, may be employed between the cam19 and the pressure plate 17 to provide a larger area of electricalcontact with the paper24.

The camera 1 takes a picture by opening shutter 4 to illuminate thephotoconductive plate 5 with the photon image to be reproduced. Thetimer switch 27 is activated to apply the operating voltage across thephotoconductive plate 5 and paper 24. In this process, thephotoconductor 5 is rendered conductive in a pattern in accordance withthe photon image thereon. The non-illuminated portions of thephotoconductor 5 remain non-conductive. The conductive portion of thephotoconductor 5 permits a large fraction of the applied voltage to beimpressed across the minute air gap and across the dielectric filmbetween the photoconductor 5 and the conductive paper backing of thepaper 24. As a result, a charge image, corresponding to the photonimage, is transferred to the charge retentive film layer of the paper24.

After the charge image is deposited on the paper 24 the timer 27 opensthe circuit and the shutter 4 is closed. The pressure plate lever ismoved to the lower position and the air pump 12 is turned off orpreferably reversed. In the case the pump 12 is merely turned off, theatmospheric pressure is released on the paper, permitting the operatorto pull the exposed portion of the paper out of the camera housing 15.In the case where the pump 12 is reversed, air pressure greater thanatmospheric pressure is produced in the space between the paper and thephotoconductive plate, thereby pushing the paper away from the plate.The paper is then pulled through the camera as previously described.Reversing the air pump 12 is preferred because the positive pushingaction on the paper breaks the residual electrostatic attraction betweenthe charged paper and the photoconductive plate, thereby preventingabrasion of the photoconductive plate as the paper is pulled from thecamera.

The charge image is then developed on the paper 24 by any one of anumber of conventional methods employing an electrographic toner. Suchmethods include liquid toner development and dry powder development.

Although the partial vacuum hold down feature of the present inventionhas been described as it is used on an electrophotographic camera, itsuse is not confined to such cameras. It is also useful for radiographiccameras, and microfilm printers employing the same principles ofoperation. The apparatus of the present invention is useful in anyelectrophotographic apparatus where nominal contact between aphotoconductive member and a charge retentive surface of anelectrographic recording web is desired.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention can be madewithout departing from the scope thereof it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an electrographic apparatus, means forming a photoconductivemember onto which a photon image is projected, means for applying apotential across said photoconductor and a separate overlaying flexibleelectrographic recording web comprising a dielectric charge retentivefilm supported on a conductive web to produce a charge image on thecharge retentive surface of the flexible recording web, the improvementcomprising, means at the marginal edge of said photoconductive memberfor drawing a partial vacuum between said photoconductive member and thecharge retentive surface of the electrographic recording web for causingatmospheric pressure at the back side of the Web to press the chargeretentive surface of said web into nominal contact with essentially theentire mutually opposed area of said photoconductive member, whereby airpockets are' prevented from being trapped between said photoconductivemember and the electrographic web, and including means for applyinggreater than atmospheric air pressure to the space between saidphotoconductive member and the electrographic recording web after thecharge image has been transferred to the recording web, whereby the webis pushed by the air pressure away from the photoconduc tive member tofacilitate removal of the web without abrading said photoconductivemember.

2. In an electrographic apparatus, means forming a photoconductivemember onto which a photon image is projected, means for applying apotential across said photoconductor and a separate overlaying flexibleelectrographic recording web comprising a dielectric charge retentivefilm supported on a conductive web to produce a charge image on thecharge retentive surface of the flexible recording web, the improvementcomprising, means at the marginal edge of said photoconductive memberfor drawing a partial vacuum between said photoconductive member and thecharge retentive surface of the electrographic recording web for causingatmospheric pressure at the back side of the web to press the chargeretentive surface of said Web into nominal contact with essentially theentire mutually opposed area of said photoconductive member, whereby airpockets are prevented from being trapped between said photoconductivemember and the electrographic web, and wherein said means at themarginal edge of said photoconductive member for drawing a partialvacuum includes, means forming an elastic gasket encircling the marginaledge of said photo- 2 conductive member and means forming a movcablepressure disposed at the back side of the web for forcing the web intopressure contact with said elastic gasket, whereby the marginal edge webis sealed in a gas-tight manner around the marginal edge of saidphotoconductive member to facilitate drawing the partial vacuum betweenthe web and said photoconductive member.

References Cited UNITED STATES PATENTS 2,283,788 5/1942 Briechle 95-12.53,115,075 12/1963 Alexander 95-1.7 3,169,465 2/1965 Patterson 95763,224,353 12/1965 Jones 9576 3,057,275 10/ 1962 Walkup 355-3 NORTONANSHER, Primary Examiner L. H. MCCORMICK, JR., Assistant Examiner US.Cl. X.R.

